A conventional vehicle control system changes over a shift range of an automatic transmission of a vehicle through by-wire control in response to an output signal from an operation unit operated by a vehicle driver. The output signal instructs the shift range to the automatic transmission of the vehicle. In the vehicle control system of this type, however, it is probable that abnormal signals are input to a by-wire control part from the operation unit due to defective operation of the operation unit or defective communication between the operation unit and the by-wire control part. Such abnormal signals will cause an unnecessary change over to a shift range different from the one instructed by the driver or make it difficult to change over the shift range as instructed.
JP-B-5-43904 proposes enhancing fail-safe performance by using an emergency switch attached to an operation unit in case the operation unit becomes defective.
However, this emergency switch is operated only in case a trouble has occurred. This is additionally incorporated in the operation unit and raises the cost. Besides although this technology can cope with the trouble in the operation unit but cannot cope with the defective communication between the operation unit and the by-wire control part, and is not still satisfactory from the standpoint of fail-safe performance. Addition of a function for dealing with the defective communication further raises the cost.